This change is inline with Microsoft's recommended guidelines for
collects
(https://msdn.microsoft.com/en-us/library/dn169389(v=vs.110).aspx).
Added generator options for csharp to:
* useCollection: Deserialize responses into and return Collection<T>
* returnICollection: For List<T> or Collection<T>, return ICollection<T>
instead of the concrete type
As a consequence of useCollection, method imputs will also change to
Collection<T>.
Updated Configuration to have a DateTimeFormat
Added Unit Tests for Configuration.DateTimeFormat
Cleaned up namespaces in SwaggerClientTest
Added an embedded resource for testing uploads
